Apparatus for immersion development



Aug. 22, 1967 M. MICHALCHIK APPARATUS FOR IMMERSION DEVELOPMENT FiledJune 9, 1965 K 3 mm V W m H M 6%25 p5? 477 A/EVS United States Patent3,336,906 APPARATUS FOR IMMERSION DEVELOPMENT Michael Michalchik,Bethpage, N.Y., assiguor to Fairchild Camera & Instrument Corporation,Syosset, N.Y., a corporation of New York Filed June 9, 1965, Ser. No.462,483 9 Claims. (Cl. 118637) This invention relates toapparatus forimmersion development and more particularly to apparatus designed forthe liquid development of electrostatic images in which conductiveparticles are suspended in the insulating carrier fluid therebydispensing with the need of a fixed electrode and eliminating thecriticality of the spacing of the electrode from the base material onwhich the image is being printed.

It is well-known in the prior art that solid areas cannot besatisfactorily reproduced by the liquid development of electrostatic orelectrophotographic images where development is attempted by immersingthe electrostatic or electrophotographic image in insulating fluid whichhas suspended therein only a toner or developer. If development isattempted in this manner it generally results in deposition of toner ordeveloper material around the edges of large letters and similar solidareas. In accordance with prior art teaching one of the methods forovercoming this problem is to maintain an electrode or groundedconductor in close proximity to the surface bearing the electrostatic orelectrophotographic image while such image is in contact with theinsulating fluid having suspended therein the toner or developer. Theelectrode has the effect of filling in the center of solid images bychanging the electrostatic lines of force which normally bend betweenthe charged and uncharged portions of the insulations. It is nowWellknown that by positioning a conductive element near the chargedsurface to be printed that the lines of force or flux from theelectrostatic image are formed into lines of force perpendicular to thesurface to be printed and the electrostatic field from the image isstrengthened and thereby attracts additional toner or developerparticles. It has therefore become common practice in the printing oflarge electrostatic or electrophotographic areas to immerse a fixedconductor in the liquid developer and to maintain the fixed or rigidconductor a predetermined distance from the electrostatic orelectrophotographic image.

The disadvantage with this prior art method of printing solidelectrostatic and electrophotographic areas is that the spacing betweenthe electrode and the base material on which the image is to be printedis critical. This problem is particularly acute in such applications asthe printing of billboards where large irregularities frequently appearin the surface to be printed. Since any irregularity in the surface tobe printed varies the spacing of the electrode from the surface to beprinted, inferior results with poor resolution have been obtained whereprinting is attempted on surfaces which have any degree ofirregularities.

In view of the prior art problems which have been encountered by the useof a fixed rigid electrode in liquid development a method has beendescribed wherein the rigid electrode is replaced by a plurality offloating electrodes which are suspended in'the liquid carrier. Thesefluidized electrodes or conductors are metallic powders' which aresuspended in the liquid carrier. This method is described in patentapplication Ser. No. 462,718, which is being filed concurrently withthis patent application.

In accordance with such method the fluidized conductors consist ofconductive particles such as iron filings which are suspended in thecarrier liquid. These conductive particles function essentially as ashield for the electrostatic image, thus dispensing with the criticalityof the ice spacing of the fixed electrode from the surface to beprinted.

The present invention is directed to an apparatus for the immersiondevelopment of electrostatic or electrophotographic images in accordancewith the method described in patent application Ser. No. 462,718 filedon even date herewith. The apparatus of the present invention basicallyincludes a gravity settling bed and a flow arrangement to fluidize theheavy particles in the liquid developer. The apparatus of the presentinvention directs the insulating carrier fluid into a pattern of flowwhich results in the suspension of the fluidized conductive particleswithin an enclosure in which the electrostatic or electrophotographicimage is immersed in order to be developed.

In view of the foregoing the primary object of the present invention isto provide an apparatus for the immersion development of electrostaticor electrophotographic images in which the apparatus maintains'insuspension in the liquid developer fluidized conductive particles whicheliminates the necessity for a fixed conductor or electrode.

A further object of the present invention is to provide an apparatus forthe immersion development of electrostatic or electrophotographic imageswhich permits the printing of large, solid electrostatic orelectrophotographic areas with good resolution regardless ofirregularities in the surface of the area to be printed.

These and further objects and features of the present invention willappear from a reading of the following detailed description of oneembodiment of the invention which is to be read in conjunction with thedrawing which level 24' with any conventional insulating carrier, liquidis a vertical cross-section through a'machine illustrating the featuresof the present invention. A

The apparatus of the present invention is designed to developelectrostatic or electrophotographic images formed in any well-knownmanner. It is essential, however, to the operation of the apparatus ofthe present invention that the surface of the base material that isopposite to the surface on which the electrostatic orelectrophotographic image is formed, be electrically conductive. As atypical example, a conductive base material, such as tinfoil, can becoated on one surface thereof with a photoconductive insulating materialwhich is then subjected to a corona discharge. A portion of the chargeis then discharged such, for example, as by exposure to a light formingimage in order to form an electrostatic or electrophotographic image. Asanother example a conductive base material such as tinfoil can be coatedon one surface with an insulating material which is not photoconductive.A point charge is. then used to trace on the insulating surface anelectrostatic image which it is desired to print. These examples aremerely illustrative of manners in which the electrostatic orelectrophotographic images are formed and which it is desired to print.As stated above, the apparatus of the present invention is designed todevelop any electrostatic or electrophotographic image with thelimitation that the surface of the base material that is opposite tothat containing the image to be printed must be conductive for a purposeto be presently described.

Referring now to the figure the apparatus of the present inventionincludes a tank 10 which must be made of a conductive material such asiron, steel, aluminum, etc. The tank 10 as illustrated is grounded for apurpose to be presently described. The tank 10 is filled to a desired11, such as kerosene, heptane, or a halogenated or nonhalogenatedhydrocarbon, particularly fluorinated hydrocarbons such as Freon TFavailable from E. I. du Pont de Nemours.

The interior of the tank 10 is divided into a plurality of compartmentssuch as 12 and 13 by means of partitions such as 14 and 15. Thecompartments are generally funnel shaped and have a neck portion 16adjacent the bottom 18 of the tank 10, and tapering walls 17 whichextend divergently from the neck 16 such that the mouth portion of thefunnel i directed toward the surface 24 of the liquid carrier 11.

The compartments such as 12 and 13 are formed by the partitions such as14 and 15 which are cone shaped in order to form the funnel shapedcompartments. The partitions 14 and 15 have walls 17 which correspond tothe walls of the compartments 12 and 13, the walls of the partitions 14and 15, however, extending from the neck portions 16 upwardly and in aconvergent manner such that the walls 17 slope toward the necks 16.

As illustrated in the figure, the neck 16 of the various compartmentssuch as 12 and 13 are interconnected with each other by means of thepassageway 19 which is adjacent the bottom 18 of the tank 10. At one endof the tank 10 the passageway 19 communicates with a vertical shaft 20which opens into the interior of the tank 10 adjacent to but below thelevel 24 of the liquid carrier 11 and approximately at the level of thetops of the partitions 14 and 15.

The insulating liquid carrier 11 is adapted to flow from thecompartments 12 and 13 through the shaft 20 into the passageway 19 andthen through the neck portion 16 back into the compartments 12 and 13,the flow being in the direction of the arrows as shown in the figure.The liquid carrier 11 is circulated continuously in this closed cycle bymeans of the pump 21 or by any other well-known means. The velocity ofthe liquid carrier flow is regulated by controlling the speed of thepump 21.

The toner or developer material is suspended in the liquid carrier 11.The particle size of the toner or developer used is preferably less thanmicrons. The volume of toner or developer in the liquid carrier 11 ismaintained by replenishing the supply of developer or toner from asource not illustrated. A metered quantity of toner or developer isadded to the liquid carrier 11 depending upon the speed and quantity ofdeveloping.

In accordance with the present invention a volume of dense andconductive particles 22 is added to the insulating liquid carrier 11 andmaintained in suspension in the liquid carrier by means of the pump 21.Thus, the conductive particles 22 are maintained in suspension by rapidagitation of the liquid carrier 11. The conductive particles arepreferably metal spheroids of metals such as steel filings, ironfilings, or powders of metal such as copper, zinc, lead, aluminum, etc.The conductive particles 22 are preferably maintained between 50 and 325mesh in size. In this size range the conductive particles 22 are smallenough to be suspended in the liquid carrier 11 and are too large toadhere to the electrostatic image to be printed.

In the apparatus illustrated it is, of course, desirable only torecirculate the liquid carrier 11 in order to maintain the conductiveparticles 22 in suspension. For this reason the entrances to the necks16 and to the shaft 20 are provided with perforated closures 23 in orderto permit recirculation of the liquid carrier 11 but which will preventthe powders or the conductive particles 22 from entering the shaft 20.

The configuration of the compartments 12 and 13 and correspondingly ofthe partitions 14 and 15 serves a twofold purpose. Since the walls 17 ofthe compartments 12 and 13 converge toward the neck 16 through which theliquid carrier 11 is discharged into the compartments 12 and 13, theconductive particles 22 will be concentrated adjacent the entrance tothe neck 16 at which the velocity of the liquid carrier 11 is greatest.Due to this high velocity of the liquid carrier 11 as it leaves the neck16 the conductive particles 22 will be constantly maintained inagitation and therefore in suspension in the liquid carrier 11. Theliquid carrier 11 will accordingly be in a condition of turbulent flowadjacent the outlet of the neck 16. Since the walls 17 of compartments12 and 13 rapidly diverge or flare apart as they extend away from theneck 16 the flow of the liquid carrier 11 will rapidly become laminar,such that a laminar flow is issued at the surface 24 of the liquidcarrier 11.

In developing electrostatic or electrophotogaphic images with theapparatus of the present invention, it is essential that the conductiveparticles 22 be suspended in the liquid carrier 11 and that the velocityof the liquid fiow be laminar and low at the image surface 24. Theelectrophotographic or electrostatic image is developed by immersion ofthe image bearing surface in the liquid carrier 11 which contains insuspension the conductive particles 22 and the toner or developer. Inthe form illustrated in the figure the electrostatic image is formed bycoating a conductive base material 25, such as tinfoil, with aphotoconductive material 26. The photoconductive surface 26 is thencharged in any desired manner with a portion thereof being dischargedsuch as by exposure to a light forming image such that what remains onthe photoconductive surface 26 is an electrostatic charge 27corresponding to the image to be printed.

The base material 25 is then moved past or through the tank 10 by meansnot illustrated in such manner that the electrostatic image 27 isimmersed in the liquid carrier 11 preferably slightly below the imagesurface 24. In the preferred embodiment of the invention the surface 28of the base material 25 which does not contain the electrostatic image27 is not immersed in the liquid carrier 11 such that it remains dry.

In order for the apparatus of the present invention to properly developelectrostatic or electrophotographic images it is necessary that thetank 10 and the conductive base material 25 be of the same electricalpotential. In order to avoid any physical interconnection between thebase material 25 and the tank 10 these components are electricallyinterconnected by grounding both the tank 10 and the conductive basematerial 25. In the case of the moving base material 25 this can be doneby means of a flexible contact (not illustrated) which maintains contactwith the side 28 of the base material 25 opposite the image 27,regardless of the variations in the movement of the base material 25.

As the image 27 is going through the liquid carrier 11 the image isdeveloped by deposition from the liquid carrier 11 onto the image 27 ofthe developer or toner suspended in the liquid carrier 11. This carrieris subsequently fixed to the surface of the base material 25 by anywell-known means, such, for example, as by the application of heat whichfuses the developer to the surface of the base material. Duringdevelopment the conductive particles 22 function as a floating or fluidelectrode which therefore obviates any criticality between the spacingof the electrode from the surface to be printed. The level of the liquidcarrier 11, i.e. the imaging surface 24, must be so related to thequantity of conductive particles 22 maintained in suspension in theliquid carrier 11 that the conductive particles 22 effectively functionas an electrode. Thus, if the concentration of conductive particles 22in suspension in the liquid carrier 11 is too small the result will beas if no electrode were present, whereas if the concentration is toogreat the result is the same as if the electrode were held too close tothe surface to be printed. It has been found that optimum results can beobtained if the volume of conductive particles such as iron in thecompartments 12 and 13 is approximately 68 percent and the insulatingliquid carrier 11 such as Freon is approximately 31.7 percent with thetoner or developer representing about 0.3 percent of the volume.

As previously explained the tank 10 and the conductive backing plate 28are grounded so as to be at the same potential. If desired a negative orpositive voltage can be applied between the tank 10 and the backingplate 28 and will result in a variable contrast image or image reversal.

What has been described is an apparatus for developing electrostatic orelectrophotographic images Without the use of a fixed electrode butthrough the use of a plurality of floating or fluidized electrodes. Thefluidized or floating electrodes consist of conductive particles whichare maintained in suspension in an insulating liquid carrier which alsohas in suspension the toner or developer.

I claim:

1. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a tank containinginsulating carrier liquid, developer particles suspended in said liquid,a plurality of conductive particles in said liquid, means for immersingsaid image bearing surface in said liquid, and means for agitating saidliquid such that said conductive particles are maintained in suspensionin said liquid and function as a floating electrode whereby saiddeveloper is deposited uniformly over the area of said image regardlessof irregularities in the surface of said base material containing saidimage.

2. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a tank containinginsulating carrier liquid, developer particles suspended in said liquid,a plurality of conductive particles in said liquid, means for immersingsaid image bearing surface in said liquid, means for maintaining saidconductive surface of said base material and said conductive particlesat the same potential, and means for agitating said liquid such thatsaid conductive particles are maintained in suspension in said liquidand function as a floating electrode whereby said developer is depositeduniformly over the area of said image regardless of irregularities inthe surface of said base material containing said image.

3. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a tank containinginsulating carrier liquid, developer particles suspended in said liquid,a plurality of conductive particles in said liquid, means for immersingsaid image bearing surface in said liquid, means for grounding saidconductive surface of said base material and said conductive particlesWhile said image bearing surface is immersed in said liquid, and meansfor agitating said liquid such that said conductive particles aremaintained in suspension in said liquid and function as a floatingelectrode whereby said developer is deposited uniformly over the area ofsaid image regardless of irregularities in the surface of said basematerial containing said image.

4. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a conductive groundedtank containing insulating carrier liquid, developer-particles suspendedin said liquid, a plurality of conductive particles in said liquid,means for immersing said image bearing surface in said liquid, means forgrounding said conductive surface of said base material while said imagebearing surface is immersed in said liquid, and means for agitating saidliquid such that said conductive particles are maintained in suspensionin said liquid and function as a floating electrode whereby saiddeveloper is deposited uniformly over the area of said image regardlessof irregularities in the surface of said base material containing saidimage.

5. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a conductive groundedtank containing insulating carrier liquid, developer particles suspendedin said liquid, a plurality of conductive particles in said liquid,means for immersing said image bearing surface in said liquid, means forgrounding said conductive surface of said base material while said imagebearing surface is immersed in said liquid, and pump means for agitatingsaid liquid such that said conductive particles are maintained insuspension in said liquid and function as a floating electrode wherebysaid developer is deposited uniformly over the area of said imageregardless of irregularities in the surface of said base materialcontaining said image.

6. Apparatus in accordance with claim 5 wherein said conductive surfaceof said base material is not immersed in said carrier liquid duringdevelopment of said image.

7. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a conductive groundedtank containing insulating carrier liquid, said tank beinglongitudinally divided into a plurality of compartments, duct meansadjacent the bottom of said tank and interconnecting said compartments,developer particles suspended in said liquid, a plurality of conductiveparticles in said liquid, means for immersing said image bearing surfacein said liquid, means for grounding said conductive surface of said basematerial while said image bearing surface is immersed in said liquid,and pump means for recirculating carrier liquid from said compartmentsthrough said duct and back into said compartments, the velocity of saidliquid into said compartments being of a magnitude such that saidconductive particles are maintained in suspension in said liquid andfunction as a floating electrode whereby said developer is depositeduniformly over the area of said image regardless of irregularities inthe surface of said base material containing said image.

8. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a conductive groundedtank containing insulating carrier liquid, said tank beinglongitudinally divided into a plurality of compartments, duct meansadjacent the bottom of said tank and interconnecting said compartments,the walls of each of said compart ments extending divergently from saidduct and terminating below the surface of the liquid in eachcompartment, developer particles suspended in said liquid, a pluralty ofconductive particles in said liquid, means for immersing said imagebearing surface in said liquid, means for grounding said conductivesurface of said base material While said image bearing surface isimmersed in said liquid, and pump means for recirculating carrier liquidfrom said compartments through said duct and back into saidcompartments, the velocity of said liquid into said compartments beingof a magnitude such that said conductive particles are maintained insuspension in said liquid and function as a floating electrode wherebysaid developer is deposited uniformly over the area of said imageregardless of irregularities in the surface of said base materialcontaining said image.

9. Apparatus for the immersion development of an electrostatic imageformed on an insulating surface of a base material the other surface ofwhich is conductive, said apparatus comprising a conductive groundedtank containing insulating carrier liquid, said tank beinglongitudinally-divided into a plurality of compartments, duct meansadjacent the bottom of said tank and interconnecting said compartments,the walls of each of said compartments extending divergently from saidduct and terminating below the surface of the liquid in each compartmentwhereby liquid enters said compartments from said duct through aconstricted opening resulting in turbulent flow of liquid adjacent saidduct but laminar flow adjacent the surface of said liquid, developerparticles suspended in said liquid, a plurality of conductive particlesin said liquid, means for immersing said image bearing surface in saidliquid, means for grounding said conductive surface of said'basematerial while said image bearing surface is immersed in said liquid,and pump means for recirculating carrier liquid from said compartmentsthrough said duct and back into said compartments, the velocity of saidliquid into said compartments being of a magnitude such that saidconductive particles are maintained in suspension in said liquid andfunction as a floating electrode whereby said developer is depositeduniformly over the area of said image regardless of irregularities inthe surface of said base material containing said image.

References Cited UNITED STATES PATENTS Mayer 117---1.7 Jones 118429 XMetcalfe et a1. 11737 Thompson 118637 Gundlach 118637 X CHARLES A.WILLMUTH, Primary Examinen 10 PETER FELDMAN, Assistant Examiner.,

1. APPARATUS FOR THE IMMERSION DEVELOPMENT OF AN ELECTROSTATIC IMAGEFORMED ON AN INSULATING SURFACE OF A BASE MATERIAL THE OTHER SURFACE OFWHICH IS CONDUCTIVE, SAID APPARATUS COMPRISING A TANK CONTAININGINSULATING CARRIER LIQUID, DEVELOPER PARTICLES SUSPENDED IN SAID LIQUID,A PLURALITY OF CONDUCTIVE PARTICLES IN SAID LIQUID, MEANS FOR IMMERSINGSAID IMAGE BEARING SURFACE IN SAID LIQUID, AND MEANS FOR AGITATING SAIDLIQUID SUCH THAT SAID CONDUCTIVE PARTICLES ARE MAINTAINED IN SUSPENSIONIN SAID LIQUID AND FUNCTION AS A FLOATING ELECTRODE WHEREBY SAIDDEVELOPER IS DEPOSITED UNIFORMLY OVER THE AREA OF SAID IMAGE RE-